Joining aluminum and aluminum alloy to titanium and titanium alloy



28, 19 H. MEREDITH JOINING ALUMINUM AND ALUMINUM ALLOY TO TITANIUM ANDTITANIUM ALLOY Filed Jan. 11, 1954 '-ALUMINUM TITANUM INVENTOR. HARLANL. MEREDiTH ATTORNEY United. States Patent Harlan L. Meredith, Norwalk,Calil:'., assignor to North American Aviation, Inc.

Application January 11, 1954, Serial No. 403,181

Claims. (Cl. 219-40) The present invention is concerned with the joiningof aluminum and aluminum alloys to titanium and titanium alloys. Theprocess of this invention is concerned primarily with the joining ofsuch metals by a combined process of welding and brazing.

The problem of joining various metals to titanium is a difficult one.The presence, on a titanium surface of a tenacious oxide coating makesit difiicult to join or weld various metals to the titanium byconventional processes. It has been found that the joining of two piecesof metal, one aluminum and the other titanium, can be accomplished by acombination of a brazing and a welding operation. Such brazing andwelding is carried out using an alternating current high-frequency inertgas are as the heating element.

The principal object of this invention is to provide a gaseouscontaminant's'by providing an inert gaseous atmo-sphere 18 therea'round.

In actual operation theinert gaseous arc torch acts to clean thesurfaces'of' both the titanium and the aluminum. This cleaning action isbest accomplished when the torch has *a non-consumable electrode and isof the process of joining aluminum and its alloys to titanium and itsalloys.

A further object of this invention is to provide a process of joiningtitanium to aluminum by means of a simultaneous welding and brazingprocess.

A still further object of this invention is to provide a process ofjoining aluminum and titanium in which a sound, high-strength joint isobtained.

Other objects and advantages of this invention will of the metals duringthe subsequent heating operation.

schematically shown element 13 represents a chilling bar usually ofcopper which is used with the disclosed apparatus to conduct excess heataway from the aluminum side of the abutting members. The chilling barfurther functions to concentrate the heat at the weld zone by reason ofthe so-called jamming effect. This efiect occurs generally at area 19when the high conductivity bar 13 is conducting heat away at a maximumrate. Further heat thus is concentrated or jammed in the weld zoneitself.

Schematically shown element 14 represents a positioning bar for holdingthe parts in relationship. An inert gaseous arc torch 15, having anelectrode 16 of the consumable or non-consumable type, provides a heatsource for the joining operation. The torch 15 emits an inert gas whichenvelops the area of joining and provides an atmosphere 17 of inert gas,preventing oxidation of the surfaces adjacent to the abutting parts ofthe titanium and aluminum. It is further important that the root portionof the weld be also protected from the detrimental effects of oxygen,hydrogen, nitrogen and other ultra-highdrequency alternatingcurrenttype. An aiumimum-base filler-metal 19, generally in rod or wire form,is-broughtWithin the inert gas are heating zone. By manipulation of theinert gas arc torch, the filler metal is added to the joint area of thealuminum work piece by welding and is added to the joint area of thetitanium work piece by. a brazing process. It can thus be seen that thetemperature proximate to the aluminum side of the desired joint must beraised above the fusion temperature of the aluminum (1220 F.) in orderto obtain a satisfactory weld. The temperature of the titanium surfaceadjacent the abutment is, of course, much less than the fusingtemperature of titanium (3300 E).

A temperature in the range of 1250l400 F. at the metal surface adjacentthe weld zone 20 is generally suitable to obtain satisfactory brazing ofthe aluminumbase filler metal to the titanium surface, and welding ofthe filler to the aluminum surface. The cleaning of the weld joint areaby the alternating current are insures a low surface tension in thevicinity of that area and enables the melted filler metal to easily flowover the titanium surface and into the root portion as at 21. It is tobe understood that the aluminum filler portions which are welded to thealuminum area :of the joint, and the filler portions which are brazed tothe titanium portion of the joint are themselves integrally fused.

Various aluminum-base wire fillers have been found to be usable in theinstant joining process. Particularly satisfactory is the 5-10 per centsilicon-aluminum alloy. Other aluminum-base fillers includesilver-aluminum as Well as pure aluminum.

The instant invention is not limited to the particular joint shown inthe accompanying figure. Conventional butt weld, T welds, and lap weldsmay be fabricated using the steps of the disclosed process. It is to beunderstood that suitable inert gases include argon, helium, or mixturesthereof.

The combined welding and brazing procedure set out in the abovedescription has been found to give satisfactory bonding of aluminum andits alloys to titanium and its various alloys. The resultant weld zoneand adjacent area of the joint are both ductile and are of relativelyhigh strength.

Although the invention has been described and illus trated in detail, itis to be clearly understood that the same is by way of illustration andexample only and is not to be taken by way of limitation, the spirit andscope of this invention being limited only by the terms of the appendedclaims.

I claim:

1. The process of joining aluminum and its alloys to titanium and itsalloys comprising the steps of placing the metals to be welded inabutting relationship, playing an inert gas heating arc over surfaceareas adjacent the abutment of said metals, heating said surfaw areas toa temperature above the fusion temperature of aluminum and below thefusion temperature of titanium with said are, and adding analuminum-base filler metal to the abutting joint edges whereby thefiller metal is brazed to the titanium metal and welded to the aluminummetal.

2. The invention as set out in claim 1 in which the root portion of saidabutting joint is protected by an inert gas atmosphere during thejoining steps.

3. The invention as set out in claim 1 in which the inert gas heatingarc is of the high-frequency alternating current type. i

4. The process of joining aluminum and its alloys to titanium and itsalloys comprising the steps of placing the metals to be Welded inabutting relationship, heating the abutting edges of the metals totemperature above the melting point of aluminum and below the meltingpoint of titanium, inert gas arc welding an aluminumbase filler metalportion to the aluminum metal at the abutting edges of the joint, andinert gas are brazing an aluminum-base filler metal portion to thetitanium metal at the abutting edges of the joint, said filler portionsbe ing integrally fused with each other to form a joint bond.

5. The invention as set out in claim 4 in which an inert gas atmosphereencloses the entire abutting surfaces of said metals.

UNITED STATES PATENTS Laise Sept. 25, Chapman Nov. 8, Meredith Feb. 15,Wassell Aug. 6, Welch June 7, Miller July 5, Herbst June 30, Martin Nov.10,

1. THE PROCES OF JOINING ALUMINUM AND ITS ALLOYS TO TITANIUM AND ITSALLOYS COMPRISING THE STEPS OF PLACING THE METALS TO BE WELDED INABUTTING RELATIONSHIPS, PLAYING AN INERT GAS HEATING ARE OVER SURFACEAREAS ADJACENT THE ABUTMENT OF SAID METALS, HEATING SAID SURFACE AREASTO A TEMPERATURE ABOUE THE FUSION TEMPERATURE OF ALUMINUM AND BELOW THEFUSION TEMPEARTURE OF TITANIUM WITH SAID ARE, AND ADDING ANALUMINUM-BASE FILLER METAL TO THE ABUTTING JOINT EDGES WHEREBY THE FILERMETAL IS BRAZED TO THE TITANIUM METAL AND WELDED TO THE ALUMINUM METAL.